For manually shiftable motor vehicle transmissions in particular, H or multiple H shift patterns having multiple shift gates and a selection gate connecting the shift gates are used for a manual shift lever to be actuated by the driver, by means of which the driver can manually select the shift gate, and can engage and disengage one of the gear steps assigned to the selected shift gate. The movement of the manual shift lever for selecting a shift gate and for shifting a gear step is transferred to a rotatable and axially movable gear shift shaft internal to the transmission, wherein the selector motion can be assigned to the axial displacement and the shifting motion can be assigned to the rotation of the gear shift shaft, or vice versa.
Known manual transmissions for motor vehicles typically have five or six forward gears distributed among three shift gates and one reverse gear assigned where applicable to a special shift gate, wherein the delineation of the shift gates to each other is relatively uncritical and incorrect shifting is correspondingly unlikely. Shift patterns of such manual transmissions are shown in the FIGS. 1 and 2.
The shift pattern of a five speed transmission according to FIG. 1 has three shift gates 2, 4, 6, and a selector gate 8 connecting the shift gates. The first and second gear G1 and G2 are assigned to the outer, first shift gate 2. The third and fourth gear G3 and G4 are assigned to the center, second shift gate 4, in which the manual shift lever 10 is automatically centered in a neutral position by spring means. The fifth gear G5 and the reverse gear R are assigned to the outer, third shift gate 6. The two outer shift gates 2 and 6 can be easily located from the center neutral shift gate by the driver without danger of incorrect shifting. In order to prevent an inadvertent engagement of the reverse gear R, with a shifting device according to FIG. 1, a shift interlock is typically provided that can be designed as a push lock, a push-down lock or as a pull ring lock.
The known shifting pattern according to FIG. 2, comprises four shift gates 12, 14, 16, 18 and the selector gate 20 connecting the shift gates. The first, outer shift gate 14 and the center shift gate 16 are assigned to the gears G1, G2 or G3, G4 as in the example of FIG. 1. In this case, the gears G5 and G6 are assigned to the third, outer shift gate 18, whereas the reverse gear R is assigned to its own shift gate 12, lying further outside with respect to the shift gate 14. Accidental engagement of the reverse gear R with a shift device according to FIG. 2 can be prevented by a shift interlock of the type described above, and also by a selector interlock, by means of which, starting from the first shift gate 14, selecting the adjacent shift gate 12 for the reverse gear R is made difficult due to an increased selection force, or is prevented by a releasable form-locking lock. Such shift and selector interlocks typically interact with the manual shift lever 22 in a shift device external to the transmission, so that the device does not require any constructive intervention in the transmission.
Due to the demands for increasingly lower motor vehicle fuel consumption, an increased number of gears is desired for the transmission because a reduction in the transmission ratio steps between the gears enables nearly constant operation of the respective internal combustion engine in a rotational speed range with a specific low fuel consumption. This inevitably results in a greater number of shift gates compared to the described shift pattern. FIG. 3 shows a shift pattern having seven or eight forward gears and one reverse gear. As seen with respect to the arrangement shown in FIG. 2, an additional shift gate 24 is disposed outside of the third shift gate 18 and to which the seventh gear G7 and, if necessary, an eighth gear G8 are assigned. With a shift pattern according to FIG. 3, during an upshift procedure from a third gear G3 or a fourth gear G4 of the second shift gate 16 there is the danger of inadvertently skipping the immediately adjacent shift gate 18 for the fifth and sixth gear G5, G6, and as a result a seventh or eighth gear G7 or G8 of the fourth shift gate 24 is erroneously engaged. This shifting error leads to a loss of tractive power and in most operating situations requires an immediate corrective shift into a lower gear G5, G6.
Whereas the delimitation of the reverse gear R, or the shift gate 12 of the reverse gear R, by a shift or selector interlock of the type described above is accepted, such a delimitation of the outer shift gate 24 allocated to the forward gears G7, G8 is judged to be unacceptable due to the associated shift delay.
A shift safety device of the type named in the preamble of claim 1 is already known from document DE 10 2009 027 533 A1 in which a next outer shift gate, adjacent to the third shift gate, can be selected only after a gear in this third shift gate has been engaged. This known shift safety device is designed for a manual transmission having a gear shift shaft, the rotation of which results in a shift procedure and the axial displacement of which results in a selection procedure. This known shift safety device comprises a blocking element integrated directly in the gear shift shaft arrangement in a manner that is constructively complex and difficult to manufacture, wherein the actual gear shift shaft is disposed directly on a central guide shaft, and the blocking element designed as a blocking ring is disposed indirectly via a bearing sleeve on a central guide shaft, and wherein this blocking ring and the end of the gear shift shaft facing the blocking ring are each provided with interacting cam-like contact contours.